1. Field of the Invention
The present invention relates to a transfer tool for holding a row of magnetic heads on a slider bar so that the magnetic heads and slider bar can be lapped by abrasive grinding with minimum row bow.
2. Description of the Related Art
In a disk drive, magnetic heads are suspended over the flat surface of a magnetic disk for writing and reading data. The magnetic heads are mounted on a slider which, in turn, is supported by a suspension for positioning the magnetic heads against the surface of the magnetic disk in a transducing relationship. When the disk is rotated in the disk drive, the slider rides on a cushion of air (an "air bearing") over the surface of the disk. The height of the slider and magnetic heads over the surface of the disk is called the flying height which may be in the order of 0.075 .mu.m.
A thin film write head includes first and second pole pieces which terminate in pole tips. The pole tips are separated by a transducing gap. The length of the gap is kept as small as possible, preferably sub-micron, so that high frequency data signals can be recorded. This increases the linear density of information written by the write head. Further, the width of the write head is kept small, less than 3 .mu.m, so that the track density of information written by the write head is high. The linear density and the track density determine the areal density of a storage medium written by the write head, which is a measure of how many bits per square inch can be written to the medium.
When the pole tips of a write head become small, it is very difficult to control the quality of the writing signal. This is because the first and second pole pieces of the write head, which terminate in the pole tips, are large. The magnetic flux carried by the first and second pole pieces must enter the pole tips without the pole tips becoming saturated. In order to accomplish this objective, the throat height of the write head must be carefully controlled. The throat height is the distance between the air bearing surface (ABS) of the head to the zero throat. The ABS is the surface of the head which is supported by the air bearing. The zero throat is the linear demarcation in the magnetic head where the pole tips transition into the larger pole pieces and is generally located at the apex of one or more insulation layers within the head. A typical throat height is on the order of 1.5 .mu.m with a tolerance of 0.5 .mu.m.
Batch fabrication of magnetic heads can be accomplished by thin film deposition of row/column array of magnetic heads on a substrate, the substrate providing slider material for the magnetic heads. Alternatively, the slider material can be fabricated also by thin film deposition, in which case the thin film deposition takes place on a wafer. After deposition of the magnetic heads, the substrate is cut into rows so that each row comprises a linear array of slider-mounted magnetic heads. Each row is then bonded to a transfer tool so that the sliders and magnetic heads thereon can be lapped with an abrasive material. Each magnetic head is reduced in size by lapping until a target throat height is achieved.
A significant problem in lapping is that the transfer tool has a slight amount of flexure regardless of the precautions taken to make it as rigid as possible. This problem makes it difficult to lap all of the magnetic heads on a row within a small tolerance (typically about 0.5 mm). Transfer tools are made of hardened stainless steel, but still flex. Without compensation, flexure of the tool causes a row to bow in various directions. This is known in the industry as "row bow". When row bow occurs, some of the magnetic heads are overlapped, while other magnetic heads are underlapped. A desired throat height is not achieved for all of the heads.
In commonly assigned U.S. Pat. No. 4,914,868, to Church et al., a transfer tool is adjusted for row bow by applying multiple discrete forces to the transfer tool. The transfer tool is a generally rectangular block which has an elongated slot forming a beam. A row of magnetic heads on slider material (hereinafter, a "slider row") is affixed to the beam. A pin extends through a hole in the block to a central location of the beam where a force can be directly applied. This compensates for negative row bow in which the slider row assumes a concave configuration. Forces can also be applied on an outer surface of the transfer tool at locations longitudinally displaced from the center location of the slider row to compensate for positive row bow, where the slider row assumes a convex configuration. Heretofore, with this prior art arrangement the desirable tolerance of 0.5 .mu.m, mentioned hereinabove, cannot be achieved.